STORM SIGNALS
From Satellites: Wind Waves
Live Data
Wind Waves (web site)
A complete list of real-time data links is located in the Space Weather Resources section.
The WIND spacecraft has a radio instrument called WAVES that has multiple functions, but includes radio measurements using a radio receiver called RAD2 that picks up radio waves in the frequencies from 1.075 MHz to 13.825 MHz. Although this does not go up to the 20.1 MHz frequency that we use in standard Radio JOVE kit receivers, we can look at the radio storms received by this instrument and sometimes see that these storms are likely to extend upwards in frequency such that they could be picked up by the RadioJOVE antennas at 20 MHz.
When you use the WIND WAVES data, you will first see the page below.
Click on "Daily Plots" in the left column, and you will see the next page.
This page allows you to select a day and the RAD2 instrument and display the plot. Since this site displays a whole day of data at once, you wont see today's data until tomorrow. The date is entered as 4 digits for the year, 2 digits for the month and 2 digits for the day. May 27, 2003 would be entered as 20030527. Don't forget to select RAD2 and click "Display Plot". You will see the following for May 27, 2003.
This is a special graph called a radio spectrogram. A radio spectrogram is just a plot of the intensity of radio emission received at a number of closely spaced frequencies as time increases. Spectrograms are often formed by having a receiver "sweep" through the frequencies. It measures the radio emission at one frequency for a short period of time then goes to the next higher or lower frequency and measures again, then the next frequency, and so on. When it reaches the highest or lowest frequency it can measure, it starts over again at the opposite end of the range of the spectrum it can measure. Usually the time intervals between one sweep through the frequencies and the next are so short that the time coverage looks continuous. The vertical axis is radio frequency and the horizontal is time.
The scale on the left side indicates intensity of emissions. The blue color means no or slight radio emissions. Red color means intense radio emissions. Note the flat lines that are often seen on these plots - like the pale blue lines - that extend horizontally across the plot. These are emissions at a single frequency or a narrow range of frequencies. This is usually man-made (radio station) emission. The vertical red or orange lines tell us there is a source that is sending intense emissions in many frequencies for a short time. The source for these is the Sun. These narrow, vertical red and orange lines are called Type III radio emissions and are usually from solar flares. If you remember from the GOES data for May 27, there were 2 M-class flares, a C-class, and then and X-class flare at the end of the day. The RAD2 spectrogram also shows four Type III events, and the last one at the end of the day is the most intense. Let's magnify a small part of the plot showing this intense event.
This plot shows the event, but the time span is only about an hour. The event is the nearly vertical red and purple streaks fading into orange and green and lasts about half an hour. Note the orange yellow streak of color (like a backslash '\') starting at 23.2 hours and curving down slowly and fading out in the middle of the plot at about 23.5 hours. This is likely a coronal mass ejection (CME) connected to this flare. The charged particles of the CME start out fast (higher frequency) but slow over time and the frequency gets lower. This is called a Type II or IV flare - it is difficult to distinguish between a Type II or IV, so they are often grouped together.
This plot was obtained from a very special place on the WIND WAVES site. On the first page of the WIND WAVES site you can choose Type II/IV Lists by year. If you click on 2003, you will see the following page.
Michael Kaiser maintains a list of all the Type II/IV flares in a table format. Type II/IV flares are most often associated with coronal mass ejections.The previous radio spectrogram is #11 in the list and was chosen by clicking on the blue 's' at the far right.
Now, we have enough information to know if a flare or CME has occurred. But we still don't know where on the Sun the flare occurred. The Latest Events web site would be our next stop.
TEACHER'S NOTE
More information is available when you click on the "Examples" button found on the web page for WAVES shown above and then read the explanation for the RAD2 example. This talks about the horizontal bands that are often seen in the spectrograms as a result of man-made interference. If you click on the image and look at the larger size image that is displayed you will note not only the horizontal bands that are mentioned in the explanation. There is also a red vertical line located at about two and a half hours on the plot. This is a typical "Type III" solar burst caused by electrons rapidly accelerated in the solar magnetic field. The electrons emit radio waves of a frequency that depends on the strength of the magnetic field where they are located at any instant. As they are accelerated away from the Sun the magnetic field strength gets weaker and the electrons emit radio waves of ever decreasing frequency. They are accelerated so rapidly however that the emission appears to be a single nearly vertical line passing through all the frequencies.
Type III bursts are the most common types of solar bursts seen at the frequencies covered by the RAD2 instrument. There are actually five types of solar bursts defined by solar scientists. Types I and V are not often seen at these frequencies so they won't be discussed further here. Types II and IV are seen at these frequencies, but are rarer than Type III bursts. Types II and IV bursts are associated with heavier slower moving particles being accelerated away from the Sun in major solar disturbances. They can be seen in spectrograms as downward slanted "swaths" of radio emission (like a back slash "\"). Examples of Types II and IV emission can be found in the "Type II/IV Lists" by year again on the Waves page mentioned above.
The Types II, III, and IV emission are all indicative of an active Sun that can affect the Earth's magnetosphere as a result. Generally, the more of these bursts there are in a given period, the more likely it is that Earth will be affected. The RAD2 Example Plot only had one clear Type III burst, so it is a relatively quiet solar activity period. If you click on the "Daily Plots", enter 20020821 as the date and click on RAD2 and then "DISPLAY PLOT", you will see a spectrogram that has many Type III bursts and is a rather active period.
Using the archive of WAVES Daily Plots you can get a rough estimate of how active the Sun is on a given date. For the latest data, however, you may have to wait for one or more days after a particular date before the daily plot for that date is available.
- NASA Official: Dr. James Thieman
- Project Manager: Don Robinson-Boonstra
- Website Manager: Bryan Stephenson